The present invention relates to a close-contact multi-layer type diffractive optical element, an optical material that is a resin used in the optical element, a resin precursor, and a resin precursor composition.
A close-contact multi-layer type diffractive optical element, in which two optical members made of an optical material are in close contact with each other and an interface therebetween constitutes a diffraction grating, has an advantage in that usage wavelength can be enlarged, and it is easy to align gratings.
In the close-contact multi-layer type diffractive optical element, for example, as described in Japanese Patent Application Laid-open No. Hei 09-127322, optical characteristics of two optical members sandwiching a diffractive optical plane are required to have a high refractive index and low dispersion, and a low refractive index and high dispersion, relative to each other. As a general existing low-refractive-index and high-dispersion resin, for example, there is a plastic for optical use described in Japanese Patent Application Laid-open No. Hei 04-366115. Regarding two optical members of the close-contact multi-layer type diffractive optical element, it is required that one of the optical members is made of a low-refractive-index and high-dispersion resin, and the other is made of a high-refractive-index and low-dispersion resin relative to the low-refractive-index and high-dispersion resin.
As an optical material used in an optical member of the close-contact multi-layer type diffractive optical element, a resin is suitable since the resin is capable of reducing weight of the element and production of the element can be realized at a low cost with mass-productivity enhanced. In particular, a UV-curable resin is desirable because it has excellent transferability, takes a short time for curing, does not require a heat source, and the like, which can further reduce the cost. However, in a resin conventionally used in an optical field, it is difficult to realize special optical characteristics of low dispersion while having a high refractive index.